Diabetes mellitus (DM) and thyroid dysfunction (TD) are two of the most common endocrine disorders encountered in clinical practice across all age groups and populations1,2. These conditions are intimately linked and can influence one another. Globally, diabetes represents a major public health concern, with the World Health Organization (WHO) estimating in 2000 that 2.8% of the global population had DM, predicting this would rise to 4.4% by 20303-4. Numerically, this translates to an increase from 171 million people living with diabetes in 2000 to an expected 366 million by 2030. This dramatic growth highlights the urgent need for continued research to address the complications of diabetes, including its significant association with thyroid dysfunction. Diabetes is a complex metabolic disorder characterized by chronic hyperglycemia, resulting from defects in insulin secretion, insulin action, or both.5 Factors such as obesity, a sedentary lifestyle, and hypertension contribute to the pathogenesis of diabetes. Autoimmune destruction of insulin-producing pancreatic beta cells causes type 1 diabetes (T1DM), leading to absolute insulin deficiency. In contrast, type 2 diabetes (T2DM), which accounts for 90–95% of all diabetes cases5, results from a combination of insulin resistance and inadequate compensatory insulin secretion. Thyroid dysfunction, meanwhile, affects approximately 6% of the general population, but its prevalence rises to over 10% among individuals with diabetes. Thyroid hormones play a critical role in regulating carbohydrate metabolism, and diabetes, in turn, affects the thyroid profile, creating a complex bidirectional relationship. When both disorders coexist, particularly when diabetes is poorly controlled, they can exacerbate health problems6-7. For instance, hypothyroidism in diabetic patients may increase the risk of recurrent hypoglycemia, while thyrotoxicosis (hyperthyroidism) can precipitate potentially life-threatening diabetic ketoacidosis. Despite these serious interactions, thyroid dysfunction often receives little attention in diabetic patients, partly because the symptoms of both diseases overlap and can obscure each other, leading to underdiagnosis or misattribution to other medical conditions. There are two primary forms of thyroid dysfunction. Hypothyroidism, the most prevalent form in adults, results from insufficient production of thyroid hormones triiodothyronine (T3) and thyroxine (T4)8. Its clinical features often include fatigue, weight gain, cold intolerance, and bradycardia9. On the other hand, hyperthyroidism, which is less common, results from excess secretion of thyroid hormones and accelerates metabolic processes. Symptoms of hyperthyroidism include unexplained weight loss, palpitations, nervousness, irritability, and excessive sweating10. These manifestations can have a profound impact on glucose metabolism and glycemic control in diabetic patients. In hyperthyroidism, increased hepatic glucose production and rapid gastrointestinal glucose absorption may worsen hyperglycemia, complicating diabetes management. In contrast, hypothyroidism slows glucose absorption and reduces insulin clearance, potentially increasing the risk of hypoglycemia in patients on antidiabetic therapy. Because of these complex interactions, careful screening and early detection of thyroid dysfunction in patients with diabetes are essential. Unfortunately, TD is frequently missed in routine diabetic care due to overlapping signs and lack of awareness among healthcare providers. Clinicians should maintain a high index of suspicion for thyroid disorders in diabetic patients, especially those with poor glycemic control or unexplained metabolic changes.11 Early diagnosis and appropriate treatment of thyroid dysfunction may improve not only thyroid-related outcomes but also stabilize glycemic status and reduce the risk of long-term complications of diabetes12. Ultimately, managing these two interlinked endocrine disorders in an integrated and systematic manner can help minimize morbidity and mortality associated with their coexistence. Considering the rising global burden of diabetes and the significant prevalence of thyroid dysfunction among diabetics, prioritizing research and awareness in this area remains critical to addressing these dual challenges of modern endocrinology13.

AIM

Study of the prevalence of thyroid dysfunction in patients with diabetes mellitus.

This observational cross-sectional study included 195 patients with type 1 or type 2 diabetes mellitus attending the outpatient diabetes clinic at Late Shrimati Indira Gandhi Memorial Government Medical College associated with Komaldev Hospital, Kanker, Chhattisgarh. Inclusion criteria were diabetes duration over 9 months for T2DM or over 1 year for T1DM, with specific diagnostic criteria applied to distinguish the two types. Patients provided informed consent. Clinical and laboratory evaluations recorded demographic data, comorbidities, and biochemical parameters, including HbA1c, anti-TPO, FT4, and TSH. Thyroid dysfunction was classified into clinical and subclinical hypo- or hyperthyroidism based on TSH and FT4 values. Positive thyroid autoimmunity was defined by anti-TPO levels above 34 IU/mL but was not used alone to define thyroid dysfunction.

Table 1: Age criteria of patients

Most T1DM patients were younger, with the majority under 40 years, while T2DM patients were older, peaking in the 51–70 age group.

Table 2: Duration of diabetes mellitus

Most T1DM patients had a disease duration of 11–15 years (21), while T2DM cases were highest in the same category (34) and 16–20 years (29). Fewer patients in both groups had a duration of ≤5 years (11 in T1DM, 15 in T2DM).

Table 3: Previous history of thyroid disease in patients

A history of thyroid disease was present in 13 (16.9%) T1DM patients and 35 (29.7%) T2DM patients. The majority in both groups, however, had no previous thyroid disease, with 64 in T1DM and 83 in T2DM.

Table 4: Distribution of BMI Categories and Blood Pressure Levels Among T1DM and T2DM Patients

Among T1DM patients, most had a normal BMI (18.5–24.9) and normal blood pressure, while T2DM patients were predominantly obese with higher rates of hypertension.

Table 5: Glycemic Profile and Control Status among T1DM and T2DM Patients

Most T1DM patients had poor glycemic control with HbA1c >9% (52), FPG ≥126 mg/dL (59), and 2h-PPG ≥200 mg/dL (64), while T2DM patients showed moderately better control with more in the HbA1c 7–9% range (50), yet a large proportion still had elevated FPG (90) and 2h-PPG (97).

Table 6: Distribution of Thyroid-Stimulating Hormone (TSH) Levels among T1DM and T2DM Patients

Most patients had normal TSH levels (68 T1DM, 104 T2DM), while subclinical hypothyroidism was observed in 8 T1DM and 12 T2DM cases, with hyperthyroidism being rare (1 T1DM, 2 T2DM).

Table 7: Prevalence of Anti-Thyroid Peroxidase (Anti-TPO) Antibodies in Diabetes Patients

Anti-TPO antibodies were positive in 14 T1DM and 25 T2DM patients, while the majority were negative (63 and 93, respectively).

Table 8: The frequencies of thyroid dysfunction of T1DM and T2DM patients without prior TD

Most patients showed euthyroidism (49 in T1DM, 68 in T2DM), while subclinical hypothyroidism was the next most common finding (8 in T1DM, 12 in T2DM), with fewer cases of clinical hypothyroidism, subclinical hyperthyroidism, and clinical hyperthyroidism across both groups.

Table 9: The frequencies of thyroid dysfunction of T1DM and T2DM patients with prior TD

Among patients with thyroid dysfunction, most had euthyroidism (7 in T2DM, 22 in T1DM), followed by subclinical hypothyroidism (5 in T2DM, 11 in T1DM), with few cases of subclinical hyperthyroidism (1 in T2DM, 2 in T1DM) and no cases of clinical hypo- or hyperthyroidism.

In our study, T1DM patients (n=77), the majority were younger, with 13 aged ≤20 years and 17 in the 21–30 age group. In contrast, T2DM patients (n=118) were mostly older, with no cases below 20 years. The 31–40 age group included 22 T1DM patients but only 2 with T2DM. Between 41–50 years, there were 14 T1DM and 8 T2DM cases. Notably, the 51–60 and 61–70 age groups showed a higher concentration of T2DM patients (39 and 68, respectively) compared to T1DM (8 and 3). This distribution reflects an earlier onset of T1DM versus later onset in T2DM.In a study by Palma et al, overall 386 patients, 82 (21.2%) with T1DM and 304 (78.8%) with T2DM, were included, which is similar to the criteria taken in our study.

In our study, a significant proportion of both T1DM and T2DM patients had a diabetes duration exceeding 10 years, with the largest groups in the 11–15 and 16–20 year ranges. This pattern reflects the chronic, progressive nature of diabetes. Similar findings have been reported by the UK Prospective Diabetes Study (UKPDS)15, where nearly half of T2DM participants had disease durations longer than 10 years, highlighting a substantial burden of long-term complications (UKPDS Group, 1998). Additionally, Kordonouri et al. (2002) described that in T1DM patients, disease durations commonly exceeded 10 years due to early onset in childhood or adolescence, consistent with our results showing a high proportion of T1DM patients with more than a decade of disease. These similarities reinforce the importance of long-term follow-up and complication screening in both T1DM and T2DM patients.

In our study, a history of previous thyroid disease was reported in 17% of T1DM patients and in nearly 30% of T2DM patients. This higher prevalence among T2DM patients is consistent with studies such as  the 17% prevalence in T1DM patients aligns with findings by Kordonouri et al. (2002)16, who reported rates of thyroid disease between 15–20% in T1DM, largely due to autoimmune mechanisms. Overall, the coexistence of thyroid disease with both T1DM and T2DM observed in our study highlights the need for routine thyroid evaluation in diabetic patients, regardless of type.

In our study, most T1DM patients (n=77) had a normal BMI (40), while T2DM patients (n=118) were predominantly obese (61). Underweight was seen only among T1DM cases (6), with none in T2DM. Regarding blood pressure, 42 T1DM patients had normal BP, compared to 21 in T2DM. Pre-hypertension was more common in T2DM (32) than T1DM (24), while Stage 1 and Stage 2 hypertension were significantly higher among T2DM patients (41 and 24, respectively) than in T1DM (8 and 4). This highlights greater obesity and hypertension burden in T2DM.

 In our study, most T1DM patients (n=77) had poor glycemic control, with 52 having HbA1c >9%, compared to 33 among T2DM patients. Well-controlled HbA1c (<7%) was seen in only 5 T1DM versus 35 T2DM patients. Fasting plasma glucose (FPG) was ≥126 mg/dL in the majority of both T1DM (59) and T2DM (90) cases. Similarly, 2-hour postprandial glucose (2h-PPG) was ≥200 mg/dL in 64 T1DM and 97 T2DM patients. A minority had normal FPG or PPG levels. Overall, these findings indicate suboptimal glycemic control in both groups, especially among T1DM.

Most T1DM patients (68) and T2DM patients (104) had normal TSH levels (0.4–4.0 μUI/mL). Subclinical hypothyroidism was noted in 8 T1DM and 12 T2DM cases. Only a few showed suppressed TSH suggestive of hyperthyroidism (1 in T1DM, 2 in T2DM).

Among T1DM patients (n=77), 14 tested positive for anti-TPO antibodies, indicating autoimmune thyroid involvement. In comparison, 25 T2DM patients (n=118) were anti-TPO positive. The majority of T1DM patients (63) were anti-TPO negative, similar to T2DM where 93 tested negative. This shows a higher prevalence of thyroid autoimmunity in T1DM but still a significant presence in T2DM. Anti-TPO positivity suggests underlying autoimmune thyroiditis in these diabetic populations.

 In our study, among T1DM patients without prior thyroid disease (n=64), 12.5% showed subclinical hypothyroidism, while in T2DM (n=83), the prevalence was approximately 14.5%. This pattern closely mirrors the findings of Palma et al. (2013)14, who reported subclinical hypothyroidism as the most common thyroid dysfunction in diabetic patients, with a prevalence of 13% in T1DM and 12% in T2DM. Both studies consistently found that overt thyroid dysfunction (clinical hypothyroidism or hyperthyroidism) was relatively uncommon, while euthyroidism remained the most frequent status. These similarities support the evidence that subclinical hypothyroidism is the predominant thyroid disturbance among diabetics, highlighting the importance of periodic thyroid function monitoring in both T1DM and T2DM populations.

In the present study, among T1DM patients with thyroid dysfunction (n=35), subclinical hypothyroidism (SC-Hypo) was the most frequent abnormality (11 cases), followed by subclinical hyperthyroidism (2 cases), with no clinical hypothyroidism or hyperthyroidism detected. Similarly, among T2DM patients with thyroid dysfunction (n=13), subclinical hypothyroidism was again predominant (5 cases), while only one case of subclinical hyperthyroidism was noted. This pattern is consistent with previous studies, such as Udiong et al. (2007)17, which reported a higher prevalence of subclinical hypothyroidism among both T1DM and T2DM patients compared to overt thyroid disorders. Their work highlighted that autoimmune mechanisms and metabolic factors contribute to mild thyroid dysfunction in diabetic populations, aligning with the trends observed in our study.

This study demonstrated that T1DM patients were younger at onset, with longer disease duration, while T2DM patients tended to be older and more obese, with higher rates of hypertension. Subclinical hypothyroidism emerged as the most common thyroid dysfunction across both groups, supporting periodic thyroid screening. Glycemic control was suboptimal in both T1DM and T2DM, particularly poor among T1DM patients. Anti-TPO positivity was more frequent in T1DM, indicating stronger autoimmune thyroid involvement. These findings emphasize the importance of integrated, long-term screening and management strategies for diabetes and thyroid dysfunction to prevent chronic complications.

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